In internal combustion engines operating under normal and severe conditions, oil-insoluble particles can form from combustion by-products and products from oxidation of the fuel or lubricant due to high temperatures and the presence of metals which promote oxidation. Although antioxidants can prevent the fuel or lubricant from undergoing oxidation, antioxidants are not always fully effective and oxidation by-products are not the only source of contamination. Thus, additives are needed which can disperse solid particulate matter and keep metal surfaces free of deposits.
Dispersants and detergents are compositions which can facilitate the suspension of oil-insoluble particles to inhibit the agglomeration and accumulation of the particles and settling out of the fluid. Dispersants may actually break up particle agglomerations and bring them into a colloidal suspension or solubilize them. Dispersants and detergents are also important in preventing insoluble matter from forming deposits which adhere to hot metal parts. Lubricating oils and fuels require dispersants and detergents to reduce or prevent formation of deposits on internal combustion engine parts resulting from sludge, varnish and lead compounds. Typically, the dispersants adsorb on the insoluble particles maintaining them as a suspension in the fluid to minimize their deposition and to maintain cleanliness of rings, valves and cylinder walls.
Refinery economics and environmental concerns necessitating conservation of petroleum crude stocks require refiners to make gasolines from lower quality heavy fractions. Although fluid catalytic cracking processes effectively crack these fractions, they produce high olefin content fuels. These fuels are designated "severe" fuels because they are not fully responsive to traditional additive products. Moreover, the presence of diolefins in these fuels can be detrimental to engine operation because they are highly reactive, forming gums and polymers easily. High gum levels cause problems because they separate out and lead to blocked fuel lines which hinder fuel flow, filter plugging, valve plugging, and formation of high sludge levels. They also form deposits on engine parts resulting in poor engine performance and breakdowns. Consequently there is a need for fuel additives which perform effectively in these "severe" fuels.